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Home , Field galaxy, Local Group

The Local

Brian Kent Cornell University AskAsk yourselfyourself……

What is the , and how does it compare to other ? How do you define a galaxy? What is the Local Group? Do all galaxies have close neighbors? What happens when galaxies collide? AA quickquick notenote onon unitsunits……

• Distances: 1 kpc = 3.08 x 1019 meters 6 36 • Mass: 10 M = 1.98 x 10 kg • Rates: 100 km/s ~ 100 kpc/Gyr AA closeclose friend:friend: OurOur MilkyMilky WayWay GalaxyGalaxy

• An Sbc galaxy that is 30 kpc in diameter AnatomyAnatomy ofof thethe MilkyMilky WayWay

•R0 ~ 8 kpc •200 billion

11 •5 x 10 M

•SFR ~ 3 M/yr •Bulge ~ 3 kpc in diameter AA usefuluseful tool:tool: RedshiftRedshift

λ − λ f − f z = obs 0 = 0 obs λ0 fobs

• Measure the shift in a spectral line – f0 is the rest frequency (λ0 the rest wavelength) • Extragalactic objects often identified by their cz measurement. • ALFALFA will cover cz = –2000 to 17000 km/s ExpansionExpansion ofof thethe UniverseUniverse • (among others) showed the Universe was expanding! cz = H d • However, there are other 0 factors to take into account in the local Universe – peculiar velocities! Deviations can be quite large depending on the galaxy, and whether it is part of a group or a field galaxy. AroundAround thethe MilkyMilky WayWay…… AroundAround thethe MilkyMilky WayWay…… AroundAround thethe MilkyMilky WayWay…… TheThe AndromedaAndromeda GalaxyGalaxy

• Sb galaxy 770 kpc from the Milky Way. • Larger, more luminous, with a larger disk scale length than the Milky Way – it even rotates faster at 260 km/s! • At least 9 known satellite galaxies – dwarf elliptical and spheroidals! TheThe AndromedaAndromeda Galaxy:Galaxy: GALEXGALEX M33M33

• Late-type ~850 kpc from the Milky Way and ~200 kpc from Andromeda • Disk scale length is around 1.7 kpc, rotating around 120 km/s. WhatWhat areare wewe missing!?!?!?!?missing!?!?!?!? WhatWhat areare wewe missing!?!?!?!?missing!?!?!?!?

THE GAS!!!!!!!!!! M33M33

• Richer in HI gas than M31 or the Milky Way – VLA doppler image show movement of the HI gas towards and away. •The HI disk extends out to 30 kpc, enough for M31 to cause tidal effects and warp the outer disk!

GalaxyGalaxy MorphologyMorphology WhatWhat dodo galaxiesgalaxies looklook like?like?

Well, it depends… GalaxiesGalaxies acrossacross thethe spectrumspectrum

M81

Radio provides a crucial part of the picture! GalaxyGalaxy TypesTypes

Galaxy Type Hubble de Vaucoulers

Spiral S, Sa, Sb… 1 through 6

Elliptical E -6 through –4

Dwarf dE, dSph

Lenticular S0, SB0 -3, -2, -1

Irregular Irr HubbleHubble’’ss TuningTuning ForkFork SpiralSpiral GalaxiesGalaxies

• Thin disks • Most have some form of a bar – arms will emanate from the ends of the bars • Other classification: 1. Relative importance of central luminous bulge and disk in overall light from the galaxy M51 2. The tightness of the winding of the spiral arms 3. Degree to which spiral arms are resolved into stars and individual HII regions M33 DwarfDwarf GalaxiesGalaxies

• Smaller size than giant elliptical galaxies •Lower surface brightness

M32 Sagittarius Dwarf IrregularIrregular GalaxiesGalaxies

• LMC and SMC are satellite galaxies of our own – disrupted by gravitational interaction with the Milky Way…

LMC and SMC IrregularIrregular GalaxiesGalaxies

• M82 – irregular • formation rate at 10 times the rate of our galaxy • Chandra X-ray image reveals hot gas flowing out of the galaxy – hot spots indicate x-ray binary stars – some of the brightest known! EllipticalElliptical GalaxiesGalaxies

•Smoothand very little structure; varying in shape • Classified by EN where N=10(1-b/a) • Large populations in clusters. • Little gas – don’t see spectral HI lines M87 TheThe LocalLocal GroupGroup

• The Local group has 41 members, ranging from large spiral galaxies to small dwarf irregulars. Most galaxies are dwarf spheriodals… TheThe LocalLocal GroupGroup

Giant spirals dSph (+dEll) dIrr dIrr/dSph GalaxyGalaxy GroupsGroups GroupsGroups ofof galaxiesgalaxies

• Galaxies can be gravitationally bound to each other, and undergo interactions and collisions. • Separations across intergalactic distances range from 50 kpc up to 1 Mpc. • Groups are important physically because one can determine a dynamical mass for the system. • ALFALFA science goals include studying the effects within the group environment – – What is the HI mass function – the mass density of a given environment? – How do unseen HI clouds/starless galaxies effect dynamics? – Are their unseen tidal remnants or debris? – What are sizes of HI disks? NeighboringNeighboring GalaxyGalaxy GroupsGroups GroupsGroups ofof galaxiesgalaxies M83M83 GroupGroup ExtendedExtended HIHI DiskDisk ofof aa BCDBCD M66M66 GroupGroup M66M66 GroupGroup

CollidingColliding GalaxiesGalaxies CollidingColliding GalaxiesGalaxies CollidingColliding GalaxiesGalaxies GalaxyGalaxy ClustersClusters ClustersClusters ofof GalaxiesGalaxies

• Around half the galaxies in the Universe are found in clusters or groups. • Cluster have a higher density than “loose” groups – brightest galaxies are S0s and ellipticals instead of spirals • Abell Catalog contains 4073 rich clusters • binds the members, as well as hot intracluster gas (seen in the X-ray) VirgoVirgo ClusterCluster

• cz ~ 1050 km/s • Δv ~ 1000 km/s !! • 1300 catalogued members!! • Most galaxies are dwarfs • Core radius ~ 500 kpc ComaComa ClusterCluster

•At cz = 6900 km/s • Four times the size of !! • Core contains only ellipticals. FornaxFornax clustercluster

• cz ~ 1400 km/s FornaxFornax ClusterCluster –– XrayXray viewview FornaxFornax –– opticaloptical ++ radioradio HerculesHercules ClusterCluster cz ~ 11,000 km/s PerseusPerseus ClusterCluster cz ~5000 km/s LeoLeo ClusterCluster

• cz ~ 6400 km/s CentaurusCentaurus ClusterCluster

• cz ~ 3000 km/s • Xray image shows gas expelled from the central member SuperclustersSuperclusters TheThe largestlargest structuresstructures inin TheThe UniverseUniverse SuperclustersSuperclusters inin thethe UniverseUniverse LocalLocal SuperclusterSupercluster PiscesPisces--PerseusPerseus SuperclusterSupercluster

Haynes & Giovanelli TheThe bigbig picturepicture

• 8800 galaxies from Springob, Haynes, Giovanelli, and Kent 2005 ! • A large collection of HI in galaxies! What to think about… What kind of galaxy am I YourYour MOTIVATIONMOTIVATION –– currently examining? studystudy thethe UniverseUniverse withwith -Where and what kind of thethe worldworld’’ss LARGESTLARGEST information can I find on this galaxy (or group)? telescope!telescope! -What is the distance? Mass? -What will new information obtained from YOUR observations tell you about the galaxy, it’s history, and even it’s future?